The present invention relates to tools for cleaning substantially flat, smooth surfaces. In particular the present invention relates to cleaning reflective mirrors of a heliostat used in concentrated solar field applications.
The operating efficiency of concentrated solar fields that utilize heliostats to collect solar energy is highly dependent upon the reflectivity of the glass mirrors. A small amount of dust, dirt or debris on the glass can reduce the output of the solar field by a significant amount. For this reason, a great deal of effort has gone into developing cleaning systems and devices for improving the reflectivity of the mirrors. For example, U.S. Pat. No. 8,726,458 describes a portable cleaning device that is driven down the rows of mirrors. Telescoping arms that support cleaning heads contact the mirrors to clean them.
Wet cleaning system such as the system disclosed in U.S. Pat. No. 8,726,458 have disadvantages. The amount of water needed to clean the glass is approximately 2 gallons per mirror, for an average size mirror of 5 feet×8 feet. In the desert areas where many solar fields are built, this amount of water causes the vegetation to overgrow, adding maintenance expense to the operation of the field. In addition, the use of cleaning chemicals and high volumes of water may have a negative environmental impact, which could lead to fines, temporary shut downs and even plant closures. Last, these systems may not clean all of the glass evenly, and the plants may not be designed so that these tractor systems can maneuver without colliding with and breaking the glass. When the tractors are driven manually, operator error can lead to further glass damage.
It would be desirable to develop a cleaning tool that uses only a small volume of pure water, and no chemicals, that restores the reflectivity of the glass to an acceptable level, such that the power plant can operate efficiently, while using the tool has a negligible environmental impact.